Residential customers of PG&E and other big utilities in California are headed for huge changes in their electricity rates under a plan disclosed late Wednesday by two state law judges, but the plan was immediately blasted by a consumer and environmental group.

The state Public Utilities Commission is scheduled to vote on Friday on a far-reaching revamp of electricity bills that could boost power rates by as much as $10 a month for 80 percent of California’s residential consumers, including those served by San Francisco-based PG&E.

Rates are expected to rise at least $10 a month for 35 percent of residential electricity customers in the state.

The new proposal, issued by administrative law judges Jeanne McKinney and Julie Halligan, quickly received harsh criticism Wednesday night.

“On the eve of Independence Day, the PUC has shown it continues to take orders from the utilities at the expense of the public,” said Evan Gillespie, director of the Sierra Club. “The proposed decision punishes low energy users, hurts low-income families and discourages conservation.”

The Sierra Club also criticized the PUC for making its decision Friday, just ahead of a long holiday weekend, and in some cases, the day that Independence Day is observed.

“It’s hard to view this move as anything other than yet another gift to the utilities when nobody’s watching,” Gillespie said.

The PUC has been blasted by critics — and is facing state and federal criminal investigations — for what some believe is a cozy relationship with PG&E, Southern California Edison, and San Diego Gas & Electric, all parties in the electricity case.

The Sierra Club called on the PUC to approve a plan floated by PUC Commissioner Michael Florio.

“We have an electricity rate structure that sort of happened by accident because of legislative decisions after the energy crisis,” Commissioner Florio said Wednesday. “The system of electricity rates that we have today isn’t really ideal.”

For about 15 years, customers who consumed less power have been paying less than it cost to supply that power by California’s three big utilities. This means that high usage residential customers are subsidizing ratepayers who use little electricity under the current system.

“The system needs to be changed, and my proposal would bring about less drastic change” compared to what the two judges have been proposing, Florio said.

The new proposal from the judges would set a minimum charge of $5 a month for low-income residential customers of PG&E. The minimum charge would be $10 a month for customers who aren’t low-income.

In addition, the two judges also proposed a surcharge for high-usage customers. It’s expected about 2 percent to 10 percent of residential electricity customers will be hit by the surcharge, which applies to those who use more than twice the electricity consumption for an average residential customer.

“We wish to ensure that those customers who consume a disproportionately high amount of energy are not rewarded,” the two judges wrote in their proposal. “This decision sets moderate rates for the vast majority of customers and implements a Super-User Electric Surcharge for those customers who use substantially more than average.”